Geochemistry and petrogenetic evolution of metasedimentary rocks in Bunu Area, part of Kabba-Lokoja-

• 作者: M. S. Kolawole E. C. Chukwu A. N. Agibe
• 来源期刊: 地球化学学报(英文）
• 关键词: Geochemical studies Metasedimentary rocks Geodynamic activities Protolith Passive continental margins
• 年，卷（期）: 2022,（5）
• 页码范围: 765-788
• 页数: 23页
• 语种: 英文
• DOI: 10.1007/s11631-022-00545-y

摘要

Field and geochemical studies of the Bunu area, SW Nigeria, were carried out on gneiss-metasedimentary rocks that consist of migmatised gneiss, quartz-mica schist, and foliated and massive quartzites. These gneiss-metasedimentary rocks are interbedded with meta-igneous rock (amphibolite), all of which are intruded by granitoid and cut by basic and felsic dykes. Geochemical data on major, trace, and rare Earth elements of these rocks from the area were used to speculate on the petrogenetic and geodynamic evolution of the rocks in the area. Compositionally, the metasedimentary rocks in the area have a restricted range of major oxides such as SiO2 and Al2O3 with low average values of Fe2O3, MnO, CaO, and P2O5. Concentrations of average values of HSFE such as Zr, Nb, and Y are moderately high in migmatitic gneiss, quartzmica schist, and low in both massive and foliated quartzite. PLREE average values are 124.25, 132.41, and 18.64 ppm respectively for migmatite gneiss, quartz-mica schist, and low in both massive and foliated quartzite. These rocks are also generally enriched in Ba, Cs, Pb, U, Cr, Rb, and Zr and depleted in Be, Sr, Ti, Mo, Th, and W. This enrichment–depletion in major oxides and trace elements of the rocks in this area is probably a consequence of the movement of metamorphic remobilized fluids within the rocks in the area during the Pan-African or earlier events as noted in the adjacent Egbe-Isanlu Schist belt. A further geochemical characterisation of the rocks in the area using Log (Na2O/K2O) vs Log (SiO2/Al2O3 indicates that while the protolith of migmatised gneiss and quartzmica schist are greywackes to litharenite in compositions that of quartzites are sublitharenite to quartz arenite. On the ternary plot of Al2O3-(CaO+Na2O)-K2O for metasedimentary rocks in the area, most migmatitic gneiss and quartz-mica schist rocks plot close to average shale while quartzites mostly tend to illite compositions and almost toward the Al2O3-apex of the diagram